Electric fuse having balanced low current interrupting performance and high current interrupting performance



Dec. 27, 1966 F. J. KozAcKA 3,294,938

f ELECTRIC FUSE HAVING BALANCED LOW CURRENT INTERRUPTING PERFORMANCE ANDHIGH CURRENT INTERRUPTING PERFORMANCE Filed OCt. 2l, 1965 Fig.

X11-Vg n for FREDERICK. ef. .RozAcBA United States Patent O ELECTRC FUSEHAY/ENS BALANCED MEW CUR- RENT INTERRUPTING PERFQRMANCE AND HIGH CURRENTINTERRUPTING PERFORM- ANCE Frederick Jrlozaclra, South Hampton, NH.,assigner to The Chase-Shawmut Company, Newburyport, Mass.

Filed Oct. 21, 1955, Ser. No. 499,743 3 Claims. (Cl. 20d-120) This is acontinuation-in-part of my copending patent application Ser. No. 474,778tiled July 26, i965, for Electric Fuse With Separate Quartz Sand FillersHaving Different Grain Sizes.

I have shown in the above patent application that in electric fusesrelatively coarse quartz sand lends itself better to interruption ofrelatively small currents than relatively fine quartz sand, and thatrelatively fine quartz sand lends itself better to interruption ofrelatively large currents, or short-circuit currents, than relativelycoarse quartz sand.

I have further shown in the above patent application that by providing afuse with two separate bodies of quartz sand, one being relativelycoarse and particularly adapted to interrupting relatively smallprotracted overload currents and the other being relatively tine andparticularly adapted to interrupting relatively large currents, orshort-circuit currents, an excellent interrupting performance `at lowcurrents as well as at high currents may be achieved.

While it is thus possible to -provide electric quartz-sandfilled fuseshaving a balanced low current interrupting performance and high currentinterrupting performance, the manufacturing cost of such fuses arerelatively high on account of the provision of two separate bodies ofquartz sand having different grain sizes and different arcquenchingproperties under different arcing conditions.

lt is, therefore, one object of this invention to provide electric fuseshaving performance characteristics similar to those of the fusesdisclosed in my above patent application, i.e. fuses having a balancedlow current interrupting performance and high current interruptingperformance, but not requiring two separate bodies of different quartzsand to achieve this end.

Another object of this invention is to provide quartzsand-filled fuseshaving but one body of quartz sand, and yet having a balanced lowcurrent interrupting performance and high current interruptingperformance.

Further objects and advantages of the invention will become apparent asthe following description of the invention proceeds, and the features ofnovelty which characterize the invention will be pointed out withparticularity in the claims annexed to, and forming part of, thisspecification.

For a better understanding of the invention reference may -be had to theaccompanying drawings illustrating the invention wherein:

FIG. l is a longitudinal section of a fuse embodying the presentinvention; and

FlG. 2 is a section along 2 2 of FIG. 1.

The structure shown in the drawings is similar to that disclosed andclaimed in the copending patent application of Philip C. Jacobs, Jr.,filed October 2l, 1965; Ser. No. 502,782, for ElectricQuartz-Sand-Filled Fuse Adapted to Interrupt Effectively ProtractedSmall Overload Currents. The above application of Jacobs discloses thata fuse having a quartz sand filler can be adapted to interrupteffectively protracted small overload currents by shunting the maincurrent carrying fusible element thereof by means of an additionalfusible element having a considerably smaller current carrying capacityand a conggflii Patented Dec. 27, 1966 ICC siderably higher resistancethan the main fusible element, the additional fusible element beingsurrounded by a a woven sleeve of glass fibers.

l have discovered that the performance of a fuse of the kind disclosedin the above patent application of lacobs depends critically upon thegrain size of the quartz filler thereof, and that by providing the fusewith a filler having a relatively fine grain size the fuse can be causedto have a balanced interrupting performance, i.e. performancecharacteristics similar to those of the dual quartz-filler-fusedisclosed and claimed in my above referred-to patent application Ser.No. 474,773.

Referring now to the drawings, numeral i has been applied to indicate asubstantially tubular casing of insulating material closed on the endsthereof by a pair of terminal elements 2 formed by caps or ferrules.Ferrules 2 are conductively interconnected by a first fusible element 3in form of a ribbon having a relatively large current-carryin-gcapacity. Fusible element 3 has preferably a plurality of seriallyrelated points of reduced cross-section and made of a metal having arelatively highconductivity and a relatively high fusing point such assilver, or copper, which metals will hereinafter be referred-to by thegeneric term high conductivity high fusing point metals. It supports inthe center region thereof an overlay 5 of tin or another metal having arelatively low fusing point and capable in melted or liquid state ofsevering the base metal by which it is supported by -a process of metalinterdiffusion involving the formation of alloys having a relativelyhigh resistivity. Ferrules 2 are also conductively interconnected by asecond fusible element 5 which has a relatively small current-carryingcapacity, i.e. the current-carrying capacity which is considerablysmaller than that of main fusible element 3. The second fusible element5 is enveloped by a sleeve o of woven glass cloth. Sleeve 6 is shorterthan fusible element or wire 5 and there is a layer of quartz sand 7between the inner surfaces of ferrules 2 and the axially outer open endsof glass cloth sleeve 6. This layer of quartz sand protects the axiallyinner surfaces of caps or ferrules 2 against jets of hot products ofarcing which may issue from the axially outer ends of sleeves 6 when thefusible element or wire 5 which is enclosed in it fuses and vaporizesunder the heat of an arc taking the place of wire 5, or of partsthereof. Fusible element or wire 5 tits loosely into sleeve 6 of wovenglass cloth, i.e. the O.D. ofwire 5 is considerably less than the ID. ofsleeve 6. The inner surface of sleeve 6 condenses the hot products ofarcing resulting from fusion and vaporization of wire 6, and for thisreason this surface should be relatively large, which is achieved by theabove relation between the 0.1). of wire 5 and the LD. of sleeve 6. Itwill be understood that the inner surface of sleeve 6 is in physicalengagement with fusible element or wire 5 at some points thereof, and isspaced from fusible element or wire 5 at other points thereof. The body7 of quartz sand inside of casing l laterally surrounds the firstfusible element 3 and laterally surrounds the sleeve 6 of glass clothenveloping the second fusible element or wire 5. In order to achieve abalanced low current .and high current interrupting performance, i.e. inorder to impart to the fuse structure a good high current interruptingability in addition to the good low current interrupting ability it hasas a result ofthe provision of the glass cloth sleeve 6 mounted onfusible element 5, the grain size of the body 7 of quartz sand must beliner than 40 US. Standard Sieve number size, preferably 50-70 U.S.Standard Sieve number size, which is coarser than US. Standard Sievenumber.

The presence of overlay 4 on fusible element 3 limits the temperature towhich the body 7 of quartz sand is heated before a break is formed infusible element 3 as a result of the flow of a protracted small overloadcurrent and an arc is kindled across that break. The presence of overlay4, therefore, greatly limits the heat absorbing duty to which the nequartz sand ller is subjected at small protracted overload currentswhich the filler as such is ill suited to interrupt, and with which itcould hardly cope successfully if the second link 5 and its glass clothsleeve 6 were not present.

The main or rst fusible element 3 may, if desired, be replaced by aplurality of fusible elements whose aggregate current-carrying capacityis high, and whose aggregate ohmic resistance is low in comparison tothe current carrying capacity or resistance of fusible element or wire5.

lt will be understood that I have illustrated and described a preferredembodiment of the invention, and that various alterations may be made inthe details thereof without departing from the invention as defined inthe appended claims.

Iclaim:

1, An electric fuse comprising in combination:

(a) a substantially tubular casing of insulating material;

(b) a pair of terminal elements closing the ends of said casing;

(c) a fusible ribbon of a high conductivity high fusing point metalhaving a relatively large current-carrying capacity conductivelyinterconnecting said `pair of terminal elements;

(d) an additional fusible element having a relatively small currentcarrying capacity conductively interconnecting said pair of terminalelements;

(e) a sleeve of woven glass cloth enveloping said additional fusibleelement; and

(f) a body of quartz sand finer than US. Standard Sieve number size butcoarser than 100 U.S. Standard Sieve number size inside said casinglaterally surrounding said first fusible element and laterallysurrounding said sleeve of woven glass cloth. 2. An electric fuse asspeciied in claim 1 wherein said fusible ribbon supports an overlay of arelatively low fusing point metal, and wherein said additional fusi--ble element is in the form of a wire loosely fitted into said sleeve ofwoven glass cloth.

3. An electric fuse as specifi-ed in claim 1 wherein said body of quartzsand is -70 US. Standard Sieve number size.

References Cited by the Examiner UNITED STATES PATENTS 661,241 ll/1900Feuerlein 200-131 X 901,261 10/1908 Reynolds et al. 200-135 1,077,3691l/l913 Roberts 200-l20 1,140,953 5/1915 Cole 200-120 2,135,166 11/1938Bussmann 200--120 2,157,907 5/1939 Lohausen 200-131 X 2,326,031 8/1943Hodnette et al. 20G-120 2,439,674 4/1948 Schuck 200-120 2,532,0781l/195O Baxter 200-135 X 2,794,095 5/1957 Kozacka 200-120 X 2,800,5547/1957 Dannenberg et al. 200-131 X 2,827,532 3/1958 Kozacka 200-135 X2,833,890 5/1958 Jacobs 200-120 X 2,856,488 10/1958 Kozacka 200--120BERNARD A. GILHEANY, Primary Examiner.

l-l. B. GILSON, Assislanr Examiner,

1. AN ELECTRIC FUSE COMPRISING IN COMBINATION: (A) A SUBSTANTIALLYTUBULAR CASING OF INSULATING MATERIAL; (B) A PAIR OF TERMINAL ELEMENTSCLOSING THE ENDS OF SAID CASING; (C) A FUSIBLE RIBBON OF A HIGHCONDUCTIVITY HIGH FUSING POINT METAL HAVING A RELATIVELY LARGECURRENT-CARRYING CAPACITY CONDUCTIVELY INTERCONNECTING SAID PAIR OFTERMINAL ELEMENTS; (D) AN ADDITIONAL FUSIBLE ELEMENT HAVING A RELATIVELYSMALL CURRENT CARRYING CAPACITY CONDUCTIVELY INTERCONNECTING SAID PAIROF TERMINAL ELEMENTS; (E) A SLEEVE OF WOVEN GLASS CLOTH ENVELOPING SAIDADDITIONAL FUSIBLE ELEMENT; AND (F) A BODY OF QUARTZ SAND FINER THAN 40U.S. STANDARD SIEVE NUMBER SIZE BUT COARSER THAN 100 U.S. STANDARD SIEVENUMBER SIZE INSIDE SAID CASING LATERALLY SURROUNDING SAID FIRST FUSIBLEELEMENT AND LATERALLY SURROUNDING SAID SLEEVE OF WOVEN GLASS CLOTH.